1. Field of the Invention:
The invention concerns apparatus for generating ultraviolet radiation of high spectral radiance whereby the radiation is produced in a discharge tube having a thermoemissive cathode and a discharge space and filled with mercury/argon; by means of a wall-stabiized direct-current gas discharge at a mercury pressure p.sub.Hg of between 5 .times. 10.sup..sup.-3 and 5 .times. 10.sup..sup.-1 Torr and a current density j of the discharge current I of between 1 and 25 A/cm.sup.2.
2. Description of the Prior Art:
Such apparatus, termed a heavy-current low-pressure UV radiation source, is known for example from U.S. Pat. No. 3,679,928. The purpose of this known radiation source is to generate UV radiation with wavelengths below 2300 Angstrom (A) in particular to be used for stimulating photochemical reactions. This known radiation source, however, has so far not found acceptance in its intended market, probably, because it tends to unstable owing to plasma oscillation, and because its power consumption in relation to its UV output is too high to allow an economically acceptable useful life.
Light-current low-pressure UV radiation sources are well known from the field of fluorescent tube technology. Thus, from U.S. Pat. No. 3,117,248, for example, a UV radiation source with a mercury-gas discharge is known whereby the mercury vapor pumped from the anode to the cathode during the discharge can flow back to the anode through a duct joining the cathode space to the anode space. A similar source is known from U.S. Pat. No. 3,617,792 in which the return duct surrounds the discharge tube concentrically.
Finally, many different kinds of mercury heavy-current high-pressure and low-pressure burners for Raman spectroscopy are also known (e.g. Brandtmuller-Moser, Einfuhrung in die Raman-Spektroskpie, Steinkopf Verlag, 1962, pp. 144-159, 284-285, 298-303). However, these burners are designed almost without exception for longer wavelengths of more than 4000 A, and are not suitable for generating radiation in the far ultraviolet. Furthermore, the known burners are predominantly intended as laboratory equipment which cannot be used in technical or industrial applications.